Are there any rules regarding amending fields whilst using multiple windows?

We are using FMP over Lan network and several users have queried that information they thought they had added to fields has apparrently disappeared. The database is a "One File/Multiple Table" system.

Is it possible that it is the use of multiple windows that could cause a problem?

What usually happens is that the user is in search mode, and that he fills up the fields thinking he is adding a new record.

Solve this by making the search mode look different from the insert/edit modes.

Another problem could be the validation of a record field. I a user cannot override the validation scheme of a specific field, and that he reverts the record to the previous state, in case of new record, it is deleted, and in case of existing record, FileMaker will rollback the record to its previous state.

About the fact that you are using multiple windows, this should not be a problem. Modifications of a same record can only be done in one window. FileMaker will generate an error message if you try to modify a record already in modification in another window.

This is the same if another user is modifying the same record from another host. FileMaker won't allow the second user to modify the record till the first one has validated the record.